fix: correct message format handling and add optimistic update params

Two P0 bugs fixed:

1. "Unknown" sender name bug:
   - Root cause: Redux slice expected action.payload.message, but API
     returns message object directly as action.payload
   - Fix: Changed sessionChatSlice.js sendMessage.fulfilled to use
     action.payload instead of action.payload.message

2. First message not appearing bug:
   - Root cause: JKChatComposer wasn't passing optimisticId, userId,
     userName parameters needed for optimistic updates
   - Fix: Added uuid import, useAuth hook, and pass required params
     to sendMessage thunk

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jam-ui/src/components/client/chat/JKChatComposer.js

@@ -1,9 +1,11 @@
 import React, { useState, useCallback, useMemo } from 'react';
 import PropTypes from 'prop-types';
 import { useDispatch, useSelector } from 'react-redux';
+import uuid from 'uuid/v1';
 import { sendMessage, selectSendStatus, selectSendError, clearSendError } from '../../../store/features/sessionChatSlice';
 import { selectSessionId } from '../../../store/features/activeSessionSlice';
 import { useJamServerContext } from '../../../context/JamServerContext';
+import { useAuth } from '../../../context/UserAuth';
 
 /**
  * JKChatComposer - Message composition component
@@ -37,6 +39,9 @@ const JKChatComposer = ({ textareaRef }) => {
   // WebSocket connection status
   const { isConnected } = useJamServerContext();
 
+  // Current user for optimistic updates
+  const { currentUser } = useAuth();
+
   // Validation and state calculations
   const trimmedText = useMemo(() => inputText.trim(), [inputText]);
   const charCount = inputText.length;
@@ -71,20 +76,23 @@ const JKChatComposer = ({ textareaRef }) => {
   }, []);
 
   const handleSend = useCallback(async () => {
-    if (!canSend) return;
+    if (!canSend || !currentUser) return;
 
-    // Send message via Redux thunk
+    // Send message via Redux thunk with optimistic update parameters
     await dispatch(
       sendMessage({
         channel: sessionId,
         sessionId,
-        message: trimmedText
+        message: trimmedText,
+        optimisticId: uuid(),
+        userId: currentUser.id,
+        userName: currentUser.name
       })
     );
 
     // Clear input on success
     setInputText('');
-  }, [canSend, dispatch, sessionId, trimmedText]);
+  }, [canSend, dispatch, sessionId, trimmedText, currentUser]);
 
   const handleKeyDown = useCallback(
     e => {

jam-ui/src/store/features/sessionChatSlice.js

@@ -289,7 +289,7 @@ const sessionChatSlice = createSlice({
 
         // Replace optimistic message with real one
         const { channel, optimisticId } = action.meta.arg;
-        const realMessage = action.payload.message;
+        const realMessage = action.payload; // API returns message directly, not wrapped
 
         const messages = state.messagesByChannel[channel];
         if (messages) {